Chemistry: Post your doubts here!

[Namehere]

can sum1 explain me the shielding effect of inner electrons?

Shielding effect plays a role in ionisation energies and therefore in reactivity. Shielding usually decreases the effective nuclear force, which makes the outermost electrons experience less of an attraction meaning the electron can be removed with more ease. Shielding effect increases as you go down the group as you have increasing number of energy levels, whereas going across the period, shielding effects usually remain rather constant.
In exam questions they usually ask for a general trend, e.g. Why is there a general increase in the first ionisation energy as you go across the period? or they ask you to compare e.g. Why is the first ionisation energy of phosphorus greater than that of sulfur? or Why is the first ionisation energy of of magnesium greater than that of aluminium?
When answering those questions you should include: distance from the nucleus, effective nuclear charge (causes the atomic radius to decrease, meaning ionisation energies are higher since the electrons are nearer to the nucleus) , increasing nuclear charge, shielding effects and interelectronic repulsion (from paired electrons).
If you know the answers to those questions you should be ok for that section.

Hope it helps.

 

[knowitall10]

agha saad
Here it is, the "A" in "Abdullah" stands for Alkanes.
"P" - polymerisation of ethene
"B" - benzene
"A" - alkenes
"H" - halogenoalkanes
"A/K" -aldehydes and ketones.
I hope this helps you.

 

[agha saad]

View attachment 31880
agha saad
Here it is, the "A" in "Abdullah" stands for Alkanes.
"P" - polymerisation of ethene
"B" - benzene
"A" - alkenes
"H" - halogenoalkanes
"A/K" -aldehydes and ketones.
I hope this helps you.

AWSUM thank u so much

 

[Jaspreet Dhaliwal]

Hi guys! Help urgently, i got my mock tommorow, please help
http://olevel.sourceforge.net/papers/9701/9701_s13_qp_11.pdf
Question 21,23,25,39,17

 

[bubbles1997]

https://www.xtremepapers.com/community/threads/general-paper-8004-post-your-doubts-here.29599/

 

[Adiizz]

Asalamualaikum!
I need help for qu 2 in novemeber 2003 paper 1
A garden fertiliser is said to have a phosphorous content of 30.0% 'P2O5 is soluble in water'
What is the percentage by mass of phosphorous in the fertiliser?
A. 6.55%
B. 13.1%
C. 26.2%
D. 30.0%

 

[daredevil]

Asalamualaikum!
I need help for qu 2 in novemeber 2003 paper 1
A garden fertiliser is said to have a phosphorous content of 30.0% 'P2O5 is soluble in water'
What is the percentage by mass of phosphorous in the fertiliser?
A. 6.55%
B. 13.1%
C. 26.2%
D. 30.0%

is the answer 13.1??
look first find out the percentage of P in P2O5
it is 62/142 *100 = 43.66%
now find out 43.66% of 30 and u will get 13.1 which is the amount of P content in 30%

 

[Adiizz]

is the answer 13.1??
look first find out the percentage of P in P2O5
it is 62/142 *100 = 43.66%
now find out 43.66% of 30 and u will get 13.1 which is the amount of P content in 30%

yes! thank you very much!

 

[danielphilip]

Can someone plz xplain this question:
A student mixed 25cm3 of 0.10mol dm–3 sodium hydroxide solution with 25cm3 of 0.10mol dm–3 hydrochloric acid and noted a temperature rise of 2.5°C.
What is the enthalpy change of the reaction per mole of NaOH?
A –209 kJ mol–1
B –104.5 kJ mol–1
C –209 J mol–1
D –522.5 J mol–1

answer:

1. First determine the moles of water
moles HCl= moles NaOH= moles water= 25X0.10/1000=2.5 exp -3
2. Calculate the heat released, Q=mcx change in Tem= (25=25) X4.18 X 2.5=522.5J= 0.5225kJ
3. Calculate enthalpy change= -(heat released)/moles water= -(0.522kJ)/2.5X exp-3 mol=
-209kJmol-1

 

[danielphilip]

Hi I'm new here,
Could someone help me please?
9701/1/O/N/02

35. the element astatine lies below iodine in Group VII of the periodic table.
What will be the properties of astatine?

1 It forms diatomic molecules which dissociate more readily than chlorine molecules
2 It reacts explosively with hydrogen
3 It is a good reducing agent

Answer is 1 only, why is 3 incorrect?

Reason 3 being incorrect: Group VII elements with the formula X2 are oxidising agents. They convert as follows:
Cl2 + 2e--> 2Cl-

Shows chlorine molecule is reduced. Chlorine is an oxidizing agent.
The strength of the oxidizing agents becomes weaker down the group from Cl2 to I2. Thefore Astatine molecule is the weakest oxidizing agent.

Iodide ion, I- on the other hand is a strong reducing agent.
2I- --> I2 + 2e
Iodide ion is oxidised to iodine molecule.

thefore Astatide ion, At- is the strongest reducing agent.

39. Which ions are present in a solution of ethanol in an excess of concentrated sulphuric acid?

1 CH3CH2O^-
2 CH3CH2O^+H2
3 HSO4^-

Why is the answer 2 and 3?

Help is very much appreciated!

answer:

 

[daredevil]

View attachment 32120
hope it helps!!!

this is just SHE isnt it? the whole setup will include the test electrode if i'm not wrong?? A star

 

[AbbbbY]

this is just SHE isnt it? the whole setup will include the test electrode if i'm not wrong?? A star

You're right.

Just add volt meter, and a similar setup on the RHS (or one with a metal electrode depending on the mixture). Then again, a labelled diagram of the standard electrode potential was asked so this is indeed what the person was looking for.

 

[danielphilip]

You're right.

Just add volt meter, and a similar setup on the RHS (or one with a metal electrode depending on the mixture). Then again, a labelled diagram of the standard electrode potential was asked so this is indeed what the person was looking for.

Hi.

I hope the candidate also adds a salt bridge to complete the circuit for the electrical circuit.

 

[AbbbbY]

Hi.

I hope the candidate also adds a salt bridge to complete the circuit for the electrical circuit.

Oh right. Totally forgot about that!

 

[daredevil]

yh well A star you can add another setup on the right side then connect these two with wires and voltmeter and add a salt bridge and u hav the complete picture
IF u need the diagram of the whole setup still then tell me and i'll post it here

 

[A star]

yh well A star you can add another setup on the right side then connect these two with wires and voltmeter and add a salt bridge and u hav the complete picture
IF u need the diagram of the whole setup still then tell me and i'll post it here

yeah please i need it cant get it for 3 weeks -_- and had been inactive on xpc too

 

[snowbrood]

i keep getting 32-30 in chemistry mcqs As can u please tell me what to do i am appearing for exam in nov

 

[daredevil]

yeah please i need it cant get it for 3 weeks -_- and had been inactive on xpc too

here u go.

 

[BAOOZHEN]

salam alaikum everyone, please I urgently ask you all for some chemistry paper 3 notes/advice/help/techniques I really need help please my exam is soon, may allah help you all

 

[Hemdon]

The compound hex-3-en-1-ol, P, has a strong ‘leafy’ smell of newly cut grass and is used in
perfumery.
CH3CH2CH=CHCH2CH2OH
P
What is produced when P is treated with an excess of hot concentrated acidic KMnO4?
A CH3CH2CH(OH)CH(OH)CH2CH2OH
B CH3CH2CH=CHCH2CO2H
C CH3CH2CHO and OCHCH2CH2OH
D CH3CH2CO2H and HO2CCH2CO2H

i get the answer as CH3CH2CO2H and COOHCH2CH2OH which is not listed....can anyone explain my mistake please!!!